The present invention relates to a boost valve device for a hydraulic cylinder and, more particularly, to a boost valve device which remarkably increases the operation velocity of a reciprocating type hydraulic cylinder under no load and can be readily incorporated in an existing hydraulic cylinder control circuit.
It is well known that the operation velocity of a hydraulic cylinder is proportional to the discharge amount of the hydraulic pump and the horse power of the pump is proportional to the discharge amount and the pressure of the pump used in the circuit.
The hydraulic cylinder is not required to provide a maximum output power throughout its advance stroke and, in general, the loading stroke thereof follows a constant idle stroke. Further, it is usual to use the cylinder intermittently with rest intervals. Therefore, in the past, in order to increase the operation velocity of the oil cylinder with a relatively small pump, it has been usual to lower the discharge pressure of the pump during the idle period to thereby increase the volume of the discharge oil and, during the load period, to increase the pressure of the pump discharge oil to thereby reduce the volume of discharge oil. In practice, there has been used a combination of a low-pressure, large-capacity pump and a high-pressure, small-capacity pump or a variable discharge pump whose discharge amount decreases with increase of pressure. As another approach, a method in which the oil discharged from the pump during the idle period is reserved in an accumulator and used during the load stroke, is also known.
In any of the conventional approaches, the circuit structure becomes large and expensive and, for this reason, such methods are rarely used in hydraulic circuits utilizing relatively small pumps. Although conventional methods are sometimes used in large size hydraulic circuits, there still remain problems of economy.
An object of the present invention is to provide a boost valve device capable of remarkably increasing the operation speed of a reciprocating type hydraulic cylinder during no load operation and thus remarkably improve the operational efficiency of the cylinder.
Another object of the present invention is to provide a boost valve device which can be readily incorporated in any existing hydraulic cylinder circuit.